Judge Richard Marks QC said: "The attack by you on Angela Best was sustained, vicious and utterly brutal. She suffered an unimaginably terrible death."

His crime was aggravated by the fact it was his third killing of a female partner and that he repeatedly lied to authorities who were monitoring him in the community.

Judge Marks said: "Such repeated offending, resulting in three separate court cases, must be almost unprecedented."

Afterwards, Ms Best’s sister Lorraine Jones accused Johnson of attempting to “play the system” to get away with murder.

She said: "This convicted murderer tried to play the system as he has successfully done before.

"He used diminished responsibility as the cause for his murderous actions.

"This time, however, he has eventually pleaded guilty to murder after 12 months since his arrest and subjecting our family to unnecessary additional trauma.

"He has shown in all cases he was clearly of sound mind. He knew what he was doing when he planned and executed the horrific murder of our beloved Angela."

Prosecutor Mark Heywood QC had told how Johnson had a violent history towards the women in his life, having been convicted of manslaughter twice before.

In 1981, he was was found guilty by reason of "provocation" of killing his wife Yvonne Johnson by pushing her off the ninth-floor balcony of their home in Wolverhampton.

Then, in 1993, a couple of years before meeting Ms Best, he was convicted of strangling his common law wife Yvonne Bennett with a belt at their home in London before trying to hang himself.

The prosecution accepted his responsibility was diminished due to depression and a personality disorder and he was handed a hospital order with restrictions at the Old Bailey.

In September 1994, Johnson was allowed out of his psychiatric unit for the first time on escorted community parole.

In mid-1995, he was given unescorted leave to spend two days a week at a City and Guilds course on furniture restoration.

It was there in 1996 that he met Ms Best, who had moved to Tottenham, north London, from Manchester.

Mitigating for Johnson, Annette Henry QC said her client was likely to die behind bars.

She said: "He does not wish to be alive. He hates himself for what happened. We recognise the devastation felt by the family members."

After being sentenced, Johnson made to stand up to leave the dock, but became shaky, sat down again and was wheeled out of court.

Camden and Islington NHS Trust, which was responsible for Johnson’s care in the community since 2004, said in a statement: "We would like to offer our heartfelt condolences once again to the family of Ms Best for their appalling loss.

"We will be inviting them to meet us, should they wish to do so, to discuss the findings of the Trust’s own independently-chaired incident report".